For many years, swimmers and divers have attempted to use various devices to improve the power and speed with which a human can move through the water. A great deal of attention has been directed to devices which are adapted to provide an improved power transmitting device for use on the feet of swimmers or divers. There is a recognition that the typical foot of a swimmer or diver represents a relatively small interactive service are for coupling power to the water and propelling the swimmer or diver. The majority of such devices, particularly the early devices, generally comprised structures and shapes adapted to imitate the appendages of aquatic animals. Such devices are generally referred to as swim fins and provide a broad relatively flexible fin portion having means for securing the fin to the swimmer or diver's foot.
While the human leg and foot strokes differ somewhat, it has been found preferable to employ a leg action in which the ankle and knee joint are maintained in a relatively fixed position while the entire leg is pivoted or rotated about the hip joint through a circular segment of travel. With conventional swim fins of the type described above, the leg action moves the fin through the water causing it to flex somewhat and produce a pressure wave which is directed in the direction generally opposite to the direction of travel. This action is known as "sculling" and while the pressure wave results in a generally forward reaction force upon the swimmer or diver and forward propulsion through the water, it requires a great deal of energy to move the conventional swim fin through the water. The need for such substantial energy is caused by the high drag resistance of the water moving about the fin to replace the water displaced by the fin movement. As a result, a very small portion of the total energy required to move the conventional swim fin through the water is actually converted into a propelling thrust.
Because divers, particularly those using underwater breathing devices popularly called scuba divers, often rely exclusively upon leg action to propel them beneath the water, the high energy requirements for leg action with conventional swim fins and inefficiency of the fin action has created a need in the art for improved swim fin devices. Recognizing this need, practitioners in the art have employed a variety of structures directed at improving the efficiency and effectiveness of such swim fins.
Several structures have been created which utilize various arrangements of vent apertures or passages through the fin blade with the object of allowing the flow of water from the high pressure side of the fin to the low pressure side to reduce swimming effort.
U.S. Pat. No. Des. 280,782 issued to Hill sets forth a SWIM FIN in which a foot receptacle is coupled to a flexible blade and a plurality of vent apertures are located between the foot receptacle and the proximate end of the blade portion.
U.S. Pat. No. 3,183,529 issued to Beuchat sets forth a SWIMMER'S FOOT-FIN WITH THRUST ACCELERATING DEVICE in which a hollow foot portion adapted to receive a swimmer's foot supports an extending blade therefrom. The blade is formed of a resilient flexible material and includes a plurality of transversely spaced longitudinal ribs and a plurality of longitudinal channels extending between the upper and lower sides of the fin.
U.S. Pat. No. 3,649,979 issued to MacNiel sets forth a SWIM FIN having a foot receiving portion and a flexible blade extending therefrom. A water intake or scoop formed in the upper portion of the fin is coupled to an exhaust opening at the lower end of the fin portion by a passage such that water is caused to flow in through the scoop portion through the passage and out through the exhaust opening during the stroking action.
While such devices provide some improvement in reduction of swimming effort, they do not increase the swimming efficiency of the swim fin.
In addition to the foregoing described devices, a number of devices have been created which are directed at reducing the stress imposed upon the swimmer's ankle which otherwise arises from the use of a conventional swim fin. While the structure of these devices varies somewhat, their general operative function is to couple the force between the swim fin and the swimmer's leg directly rather than through the swimmer's ankle.
U.S. Pat. No. 3,978,587 issued to Shamlian sets forth a SWIM FIN INCLUDING MEANS FOR MAINTAINING FOOT AND LEG IN FIXED RELATIONSHIP sets forth a foot mounted swim fin adapted for fitting to the swimmer's legs having a foot receiving portion and a blade extending forwardly therefrom. The foot receiving portion includes an attachment extending rigidly therefrom at a predetermined fixed angle which when worn by the swimmer provides a fixed angle brace portion between the swimmer's foot and the swimmer's leg.
U.S. Pat. No. 4,017,925 issued to Shamlian sets forth a SWIM FIN INCLUDING MEANS FOR RESTRICTING ANKLE MOVEMENT in which a swim fin having a foot pocket and an outwardly extending fin member includes a leg cuff adapted to be fitted to the lower portion of the swimmer's leg. A rigid couplinq extends from the foot portion to the leg cuff and provides a fixed constraint of ankle movement by the swimmer.
While such ankle supporting devices permit an increased force to be applied to the fin without overly stressing the swimmer's ankle, such increased force has been found to simply increase the velocity of the swim fin through the after which in turn increases the drag or resistive force of the water upon the swim fin with the result that swimming efficiency is not significantly improved.
Several swim fin structures have been provided which generate forward propulsion or thrust through a planing action as opposed to the pressure wave action of the foregoing described types of swim fins. The primary departure of such structures from the prior swim fins is the provision of an articulating plane member which is pivotally mounted within a supporting frame which in turn is secured to the swimmer's foot.
U.S. Pat. No. 3,665,535 issued to Picken sets forth a SWIM FIN having a foot receptacle and an extending support coupled to the toe portion thereof. The extending support in turn supports a pivotally articulated blade member having a generally planar configuration. Means are provided for limiting the pivotal motion of the blade to a predetermined range of angular movement In an alternate embodiment a flexible frame is used which undergoes angular rotation about the top portion of the foot receptacle during the swimming stroke.
U.S. Pat. No. 4,209,866 issued to Loeffler sets forth a SWIM FIN in which a blade portion having a generally planar configuration is pivotally mounted to a foot section along a pivot line intermediate the leading and trailing edges. The blade is spaced from the foot portion to create a flow passage between the toe portion of the foot portion and the blade. A resilient link is coupled between the leading edge of the blade and the toe portion to restrict the angular motion of the blade.
Such swim fins avoid a substantial portion of the inherent drag provided by the above-described swim fin designs. However, the efficiency of the fin remains limited.
While several of the foregoing described swim fin structures provide some increase in swim fin efficiency and have to some extent improved swim fin design, there remains a need in the art for a further improved swim fin construction which significantly reduces the resistance of the swim fin to movement through the water while providing a higher efficiency in converting the force applied by the swimmer's leg into a forward thrust or propelling force.